Technical Field
The present invention relates to an optical pressure-sensitive adhesive sheet. More particularly, the present invention relates to an optical pressure-sensitive adhesive sheet used in lamination of an optical member, manufacture of an optical product, or the like. Further, the present invention relates to an optical film and a display device which includes the optical pressure-sensitive adhesive sheet.
Background Art
Recently, in various fields, display devices such as a liquid crystal display (LCD) or an input device such as a touch panel, which is used by combining with the display device has been widely used. In manufacturing of the display device or the input device, a transparent pressure-sensitive adhesive sheet (pressure-sensitive adhesive tape) is used for laminating an optical member. For example, the transparent pressure-sensitive adhesive sheet is used for laminating the touch panel and various display devices or optical members (e.g., a protective plate) (for example, see Patent Documents 1 to 3).
As the application of the display device or input device is expanded, the pressure-sensitive adhesive sheet used in these devices requires not only to have transparency but also to sufficiently exhibit characteristics as the pressure-sensitive adhesive sheet under various environments. For example, adhesive reliability at a high temperature, such as a high pressure-sensitive adhesion property at a high temperature or a property that does not generate foam or release at a high temperature (antifoaming release property), is required. For example, like a cellular phone having a waterproof function, in the pressure-sensitive adhesive sheet in products used even under humidified conditions (for example, high temperature and high humidity condition), it is required that white turbidity should not occur, an appearance of the display device or input device should not be degraded, and visibility of a display part of the display device should not be decreased, due to humidification.
In response to the above requirements, a pressure-sensitive adhesive in which white turbidity caused by the humidification is suppressed has been proposed (see Patent Document 4). However, although the pressure-sensitive adhesive sheet including the pressure-sensitive adhesive does not deteriorate the appearance or visibility of the display device or input device, there is a problem in that adhesive reliability is decreased at a high temperature because the pressure-sensitive adhesive force is insufficient at a high temperature, thereby causing foam or release.    Patent Document 1: JP 2003-238915 A    Patent Document 2: JP 2003-342542 A    Patent Document 3: JP 2004-231723 A    Patent Document 4: JP 2004-263084 A